This invention relates generally to two-way annunciator signaling and communication display systems, and more particularly to a system employing a plurality of identical transmitter-receiver units, each capable of communication with the others over available power distribution lines or other minimum available transmission media that is usually avoided because the inherent interference and low signal-to-noise ratio generally results in unintelligible communications.
Annunciator communication systems are well-known and are often used in hospitals, large retail establishments, industrial plants and other general business offices. Nearly all presently available communications systems are linked together by a cabling system, the size and complexity of which depends principally upon the number of stations in the system. If it is desired to enlarge or alter the system, it is obviously necessary to install additional cabling or to re-route existing cabling, often a very complex and costly task. Service of such systems is likewise difficult and costly.
U.S. Pat. No. 3,918,000, assigned to the assignee of the present invention, describes an annunciator system that does not require interconnecting communication cables but makes use of the AC power distribution lines for its data signal link. While that system is quite adequate for many applications, it is extremely complex and involves the use of many integrated circuit components as well as passive components. Furthermore, that system does not digitally reject signal perturbations but depends solely on its analog circuitry to filter out unwanted noise and interference.
The system of the present invention also makes use of the AC power lines but employs commercially available LSI components that incorporate circuitry that recognizes and rejects signal perturbations, both analog and digital, thus assuring reliability under noise and interference conditions that would render the prior art systems inoperable.
The present system includes a plurality of identical transmitter-receiver units, each of which is physically small and may, if desired, be mounted to the wall near an existing electrical outlet which provides both the power to the unit and the communication link to the other units. Each unit may have the appearance of a small hand-held calculator in that it is provided with a six-digit LED numeric display and a 12-key keyboard containing numeric keys 0-9, a CLEAR key, and an ALARM key. As will be described in detail, the internal circuitry of each unit has a capacity for handling much more data that can be displayed on the six-digit display, thus additional signaling or communications may be available if desired.
To operate the signaling and communication system of the invention, the operator merely keys in the desired addressee and message, which are represented by a number code and which are displayed on all units, including the transmitting unit. The unit will display six digits of 10 numbers each, or a total of one million combinations. The particular numbers displayed will represent a code known only to those employing a particular system, thus assuring the security of the communications. For example, the first two numbers of the six-digit message may represent the station or employee number of the addressee; the second two numbers displayed may constitute a message, such as "come immediately to"; and the third pair of numbers may represent the station of employee number of the sender. After the full communication is keyed in to the transmitting unit, the operator may then depress the ALARM key, labeled "A", and a small buzzer sounds in each unit. When the addressee receives his displayed communication, he will depress a CLEAR key, labeled "C", which will clear his display as well as all other units which displayed the message. In this way, the addressee acknowledges receipt of the message and the sender will be assured that his message was received. If the addressee does not clear the system, the sender may continue to depress the alarm key in an attempt to attract the addressee or, the sender may elect to clear the system by depressing his clear key, thus removing the message from all displays.
Briefly described, each unit of the system includes a keyboard coupled to a digital encoding circuit which applies the encoded message into the input holding register of the transmitting section of a commercially available integrated circuit chip known as a universal asynchronous receiver/transmitter, or UART, which serially transmits a binary word representing each keyed-in number. The receiver section of all units, including the transmitting unit, contains complex circuitry for rejecting input noise and distortion, and receives, shapes, and loads the signal into a register which shifts it out, in parallel, through a decoder and multiplex circuit to a commercially available integrated circuit calculator chip which controls a conventional six-digit numeric LED display.